1. Field of the Invention
The invention generally relates to a conversion device and a method thereof, and more particularly, to an analog-to-digital conversion device and a method thereof.
2. Description of Related Art
In an optical storage system, an optical pick-up head detects radio frequency (RF) signals and servo signals reflected by the surface of an optical disc. In addition, the RF signals and the servo signals are processed by an analog front-end (AFE) and converted into digital information by an analog-to-digital converter (ADC), so as to be processed by a read channel and a digital front-end (DFE). Herein the read channel may be a partial response maximum likelihood (PRML) circuit. In the procedure described above, the ADC is a critical device. The processing result of the PRML circuit and the DFE will be affected if distortion is produced in the conversion procedure.
FIG. 1A is a diagram illustrating an ideal conversion curve of an ADC. As shown in FIG. 1A, along with the increase of the analog voltage, the digital codes converted by the ADC present a monotonic increase. Strictly speaking, the ADC is only considered as an ideal ADC when the integral nonlinearity (INL) error and the differential nonlinearity (DNL) error of the ADC are zero. Thus, in an ideal analog-to-digital conversion situation, when an analog sine wave is input, the obtained digital codes present a curve similar to the sine wave.
However, in an actual application, the conversion curve of an ADC may present a non-monotonic increase. FIG. 1B is a diagram illustrating a non-ideal conversion curve of an ADC. As shown in FIG. 1B, when an analog sine wave is input, the obtained digital codes are distorted and accordingly cannot present a curve similar to the sine wave. In this case, the distorted digital codes will affect the disc reading performance of the optical storage system or reduce the error correction capability thereof. In an even worse case, a servo control failure may be caused and the optical storage system may not be able to read a disc.